By Stephanie Stahl

TRENTON, N.J. (CBS) — The United States has reached a COVID-19 milestone with 200 million people now fully vaccinated. Even with that, cases are spiking again and in locations where vaccinations rates are high. That includes many locations in the northeast.

New Jersey has the highest number of COVID-19 cases it’s had since April. Officials there are encouraging boosters following positive news Wednesday from Pfizer. They say the surge in cases is fitting a holiday pattern.

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“We have experienced, as we expected and predicted, a post-Thanksgiving spike,” Gov. Phil Murphy said.

Murphy says the latest COVID-19 cases show a dramatic increase in New Jersey’s seven-day average for new positive tests. The average increased 63% from a week ago and 198% from a month ago.

“The combination of colder weather, going indoors and then layering on top of that, a uniquely American holiday, we believed that combination is what’s driving what we’re seeing here,” Murphy said.

New Jersey is also seeing an increase in COVID-19 hospitalizations and deaths, with the vast majority among people who are not vaccinated. Most cases are from the delta variant. There is still just one confirmed omicron case, but more are expected.

“Let’s avoid hysteria,” Murphy said. “The science is incredibly incomplete.”

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Murphy says he’s encouraged with Pfizer’s new data showing a booster dose of its vaccine provides significantly more protection against omicron, compared to the initial two shots.

New Jersey is now averaging about 35,000 boosters a day, but two-thirds of residents who are eligible still haven’t received one.

“The added protection of a booster is not a bonus, it’s a necessity,” Murphy said.

There are new concerns about hospital staffing shortages. With a growing number of patients expected, the governor is urging caution with holiday festivities.

“If you’re in a crowd, whether it be in a store buying presents or in a bar, a restaurant, or a party, it is safest and wisest to mask up,” Murphy said, “especially if you do not know the vaccination status of those around you.”

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There has also been an increase in the number of COVID outbreaks in schools in New Jersey, but the governor says he’s not considering mandating vaccines for children.

Stephanie Stahl