Virus titers in the lung of vaccinated and control mice after challenge with A/Puerto Rico/8/1934 (H1N1) virus.

<p>Mice were euthanized on day 3 (white bars) and day 7 (gray bars) and brochoalveolar lavage (BAL) washes were collected. Titers are given as the averages of three BAL washes except for those harvested from group 8 on day 3 and 7 and from groups 5 and 9 on day 3, for which only 2 BAL were available. Only one BAL was harvested from group 9 on day 3. Groups 1–6 were given single vaccinations. Groups 1–8 were given two vaccinations (three weeks apart) of the same mass with each injection. Groups 1, 7, and 11 were given 15 µg rHA, groups 2 and 8 were given 5 µg rHA, and groups 3, 4, and 9 were given 1.7 µg HA. Groups 5, 6, and 10 were given placebo injections. Groups 4, 5, and 11 were given vaccinations formulated with adjuvant. Results are shown as mean ± SD virus titers in (BAL) washes. *Statistically significant decreases in titers as compared with placebo are indicated. Limit of detection is 10^1.5 TCID₅₀/ml.