Vaccine maker Sanofi Pasteur ate crow yesterday with its recall of four batches of H1N1 baby shots--800,000 shots in all. It was not clear how many of the vaccines had been administered before the recall went out.

The good news is that the recall has nothing to do with safety, but concerns a small dip in vaccine potency that health officials say is no cause for worry.

All vaccine makers hold back samples of each lot they ship and over the ensuing weeks, test samples to ensure that their potency remains high. At the time of this follow-up testing, the lot samples in question had dropped below a predetermined limit. And, so, the recall.

How might this affect your child's protection against H1N1?

Not at all if your child is age 3 or older or was immunized with either the nasal-spray vaccine or the type of injectable vaccine packaged in multi-dose vials (the type used at most flu-shot clinics).

The recall involved only thimerosal-free baby shots in prefilled syringes.

But even babies and toddlers who received one of the sub-par shots will be fully protected so long as they complete the two-dose immunization regimen recommended for all children under age 10, says Anne Schuchat, director of the National Center for Immunization and Respiratory Diseases. (These two doses are administered approximately one month apart.)

Still want more detail, even lot numbers? Visit the recall answer page set up by the Centers for Disease Control and Prevention.

A new study comparing kids in the U.S. and the Phillipines has confirmed that growing up in a too-clean environment can boost inflammation levels, which in turn may increase the risk of heart disease and other chronic ills in adulthood. So is it still a good idea to get our kids to wash their hands all the time to prevent the spread of H1N1 and other cold and flu germs?

Coincidentally, this week two housemates familiar with my book Good Germs, Bad Germs emailed me with the hope of resolving just this debate over H1N1 and hand washing. Their household includes a 5-year-old as well as an adult with a donated kidney.

Housemate #1 had been urging the five-year-old to wash her hands frequently "to prevent the spread of too many germs," including H1N1. Housemate #2 countered that the germs that ended up on the child's hand were good for her--helping her build up resistance to disease.

The title of Good Germs, Bad Germs goes right to the heart of their question. So I'm glad to offer my two cents, based on the research of immunologists and infectious disease specialists.It's true that exposure to "germs" (i.e. viruses and bacteria) is necessary to strengthen and balance the developing immune system. This appears to be most important in early childhood.

Fortunately, this exposure doesn't have to involve the kind of germs that make you sick. In fact, the vast majority of germs in our environment are harmless. They're in our water, on our pets, in good, old fashioned dirt, everywhere. And that turns out to be a very good thing. Our world and our bodies could not functional normally without them.

By contrast, only a tiny minority of the viruses and bacteria we encounter each day make their "living" by causing disease. That said, this rogue's gallery includes some nasty characters, with the H1N1 influenza virus now among them. Such "bad germs" are definitely worth avoiding.

Bottom line: With H1N1 circulating widely in our communities, the experts agree that it's definitely a good idea for everyone to wash hands frequently or use an alcohol-gel sanitizer.

This is most important after being around other people who might be infected. Someone carrying H1N1 touches something (school desk, office keyboard, doorknob, etc.) and deposits the virus. You touch that something and then touch your eyes, nose, or mouth and, bingo, that virus has found a new home.  

Frequent hand washing is even more important if you live with anyone with an immune-compromising condition. This includes organ recipients, who must take powerful immune-suppressing drugs to prevent their bodies from rejecting the donated organ. 

Science journalist Jessica Snyder Sachs is the author of Good Germs, Bad Germs: Health and Survival in a Bacterial World. Got a question or comment about swine flu? Post it here. Throughout the flu season, Jessica will be answering your questions on all things influenza.

Headline writers are spinning away with the news of a dip in H1N1 influenza, or swine flu, outbreaks.

But any suggestion that H1N1 has peaked is premature, CDC officials say. In fact, the CDC has long predicted that H1N1, like most flu strains, will hit our communities in waves. And some of the states coming late to the H1N1 party remain on their first upsurge.

Even in places experiencing a lull, flu infection rates remain higher than usual for this time of year, cautions Anne Schuchat, director of the CDC's National Center for Immunization and Respiratory Diseases. In the best case scenario, vaccination efforts--now in full swing--will blunt any future waves.

What's more, as H1N1 ebbs, seasonal flu could come roaring in, Schuchat says. Now at minimal levels, season flu typically peaks in late December and January.

Of course, there's nothing typical about this year's flu season. With H1N1 infections continuing through the summer, the previous flu season simply merged into the present one.

Of one thing we can be sure: With millions of families getting together for Thanksgiving this week, there's sure to be some viruses exchanged along with the kisses and good food.

To help counter holiday flu spread, the CDC has launched a Traveler Health Campaign.  

It's four-step strategy is pretty basic:

• Travel only if well

• Wash hands often

• Cover coughs and sneezes with tissue or sleeve

• Get vaccinated 

Happy Thanksgiving, everyone!

Related links:

7 Common Myths about Swine Flu

A History of Flu Pandemics 

Swine Flu Survival Guide

Science journalist Jessica Snyder Sachs is the author of Good Germs, Bad Germs: Health and Survival in a Bacterial World. Got a question or comment about swine flu? Post it here. Throughout the flu season, Jessica will be answering your questions on all things influenza.

Yesterday I breathed a sigh of relief as I watched my teenage daughter get her H1N1 shot at a local public health clinic. Though she grumbled as I dragged her across town during her lunch period, she couldn't help smiling when she saw it was a girlfriend's mom, a volunteer nurse, administering the shots.

In fact, there was such an upbeat community spirit around the event--organized in the meeting room of a local arts center--that I half expected someone to break out doughnuts.

We'd arrived early after getting a heads-up from the town health officer that within 24 hours of his announcing the four-hour clinic, he had received hundreds of calls from as far as two states away. Yet it was so well organized that my daughter was in and out and back to high school with 15 minutes of her lunch period to spare.

Meanwhile, on Nov. 3, CDC officials announced the availability of another 31.8 million doses of H1N1 vaccine, bringing the total doses available for distribution to 10 million. This remains short of the national need, but should make headway in vaccinating high-priority groups such as pregnant women, children and young adults, and those with underlying health problems such as asthma or heart disease.

As the ranks of the vaccinated expand well into the millions this week, health officials also expect the inevitable. After being immunized, some people will suffer health problems for reasons that have nothing to do with the vaccine. For decades, the tendency to link such events to immunization has plagued childhood vaccination programs.

As a proactive measure, an international team of epidemiologists, immunologists, and infectious-disease specialists has published a report in the medical journal Lancet, cataloging the background rates of disorders that they suspect could be erroneously linked with vaccination. Their statistics include the following:

• Miscarriage occurs in around 400 in a million pregnant women in any given day.

• Guillain-Barré paralysis occurs in around 4 in 10 million persons in any given week.  

• Sudden unexplained death occurs in 5 or 6 per 10 million persons in any six-week period.

Only if rates spike above these numbers, the researchers say, should any potential link to vaccination be proposed.

And now that I have my daughter's H1N1 shot checked off, I'm resuming my hunt for seasonal flu vaccine in our area. So far, no luck.

Science journalist Jessica Snyder Sachs is the author of Good Germs, Bad Germs: Health and Survival in a Bacterial World. Got a question or comment about swine flu? Post it here. Throughout the flu season, Jessica will be answering your questions on all things influenza.

Swine flu parties are still in the news. And on the Internet, the topic has gone viral (sorry). A search on the phrase produces over 3.3 million hits.

Still, I have to wonder whether this buzz reflects media frenzy rather than any real indication that people are deliberately exposing their children and themselves. As a reality check, I'd love to hear from any reader who has actually participated in such a party or knows people who did--and why.

At the least, a number of surveys this month indicate that many people are feeling complacent. At this point, only a minority of respondents say they will definitely get the H1N1, or "swine flu," vaccine. Admittedly, the majority of those who get sick do recover with nothing worse than a miserable week in bed.

But a new Canadian study backs up those early, scary reports out of Mexico--the ones indicating that this flu was proving deadliest among otherwise healthy adolescents and young adults--especially young women.

The researchers focused on 168 critically ill H1N1 victims in Canadian intensive care units between April and August. Septic shock and organ failure were common. Over 80 percent ended up on mechanical ventilators, or breathing machines. And 29, or 1 in 6, died. Their average age? 32. Nearly a third were previously healthy children.

"Our data suggest that severe disease and mortality is concentrated in relatively healthy adolescents and adults between the ages of 10 and 60 years," the researchers conclude in a report released in advance of its November publication in the Journal of the American Medical Association.

The twist here is that these patients started out with what seemed like "ordinary" flu symptoms--the kind that public health officials tell us to treat at home. The difference was that their symptoms took a sudden and terrible turn for the worse.

This inability to tell who will or won't develop life-threatening complications seems to underscore the paramount importance of prevention. Vaccine party, anyone?

Science journalist Jessica Snyder Sachs is the author of Good Germs, Bad Germs: Health and Survival in a Bacterial World. Got a question or comment about swine flu? Post it here. Throughout the flu season, Jessica will be answering your questions on all things influenza.