BA.5 is the most contagious form of COVID yet. What happens next is up to us.

Over the July 4th weekend, Citizens Bank Park was filled to capacity; I was among the more than 43,000 fans there to see the Phillies play (they won) and see fireworks. What I didn’t see was a mask on more than a handful of the tens of thousands of faces all crammed together.

One would never know that we were still in the middle of an ever-changing COVID-19 pandemic, with a large and increasing proportion of the population still vulnerable to an ever-mutating, immune-evading virus.

According to the latest data from the CDC, the dominant strain causing COVID-19 is now the BA.5 form of the omicron variant of the virus. Have you noticed more people recently saying they have had COVID-19, and reports of hospitalizations and deaths ticking up? That’s likely due to BA.5.

There’s a lot we don’t know about BA.5. However, we have determined that it’s the most contagious version of the COVID-19 virus we’ve seen so far, which means it infects people more easily than past forms of the virus. (And some infectious-disease experts think that it may even be more transmissible outdoors than other forms of the virus, depending on the circumstances such as at a crammed baseball stadium, although I haven’t seen specific studies to support this.) Because it’s so different from the original virus strain forming the basis of the current vaccine, vaccination and past infection with the virus are less protective against new infection. Luckily, we do not yet have evidence that it causes more severe disease; any increase in hospitalizations or deaths could simply be the result of more cases, not that this form of the virus is more deadly.

Still, the next few months may be hard to predict. The fireworks that followed the Phillies game over July 4th weekend were perhaps a metaphor for what we could experience with the pandemic in the fall.

» READ MORE: Why BA.5 is not a super-virus, and how the vaccines are still the best option against COVID

Predicting what will happen with the virus and its impact on the population is fraught with uncertainty, as our experience in the last 2½ years (and recent modeling by experts) has shown.

What we do know is that, even though the dominant viral strains continue to drift away from the original strain, our vaccines — especially with booster doses — still provide good protection against severe disease and its complications.

Now that BA.5 is here in full force, we need to stay vigilant. This means following vaccination recommendations and all the other ways we can prevent infection, such as improving indoor ventilation in schools and wearing masks when in crowded public settings where the vaccination status of individuals is unknown, and likely not up-to-date.

“For many of us, it’s time for a booster.”

For many of us, that means it’s time for a booster. When a second booster was first recommended in April, I initially opted to wait, even though I was over 50. Cases were relatively low, I was in good health, and I wanted to save my second booster for when I’d most likely need it. I ended up getting it in June so that I could attend a four-day conference later that month. (Despite the requirement that all approximately 1,500 attendees be vaccinated and wear masks at the meetings, 19 people were diagnosed with COVID-19 during or soon after the conference.)

However, less than half of fully vaccinated people in the United States have gotten one booster shot — and only around one-quarter have received two.

We need to work on that, as well as the rate of vaccinations among children between 6 months and 4 years of age, who became eligible last month. These vaccines can prevent illness not just in children but also among all the adults in their lives, many of whom may be vulnerable to severe illness and death — this is even more true now, since BA.5 became dominant.

We need to keep encouraging public health officials, health-care practitioners, and caregivers to vaccinate children over the summer before returning to a school environment, where COVID-19 can spread more easily.

Last month, following the FDA’s vaccine advisory committee’s advice, the agency required that future booster doses should be updated to be more effective against BA.5 and a related version, BA.4. The challenge now is to develop and produce this new formulation quickly, and in sufficient quantity, to vaccinate the public before an expected COVID-19 upsurge in the fall. (And hope that it will still be helpful by then, given the rapid evolution of the virus, and that people will actually get it once it’s available.)

So there’s a lot we can’t predict. But thinking all is well, and that we can forgo vaccines and throw out our masks, is not a protective option. We need to take steps now to prevent an explosion of cases in the cooler months when we move indoors.

Eddy Bresnitz is a physician and former deputy commissioner of the New Jersey Department of Health, where he was also the medical adviser to the COVID-19 Response Team. dreddybres@gmail.com